Detection of the motor points of the abdominal muscles

Abdominal functional electrical stimulation (AFES) is a technique intended to improve respiratory function in tetraplegia where breathing is affected due to abdominal muscle paralysis. Although it is known that optimal muscle contraction is achieved when electrical stimulation is applied close to the muscle motor point, AFES studies have used a variety of electrode positions. This study aims to investigate the feasibility of using Neuromuscular Electrical Stimulation to detect the motor points of the abdominal muscles, and to evaluate the intrasubject repeatability and intersubject uniformity of their positions, to find the most suitable AFES electrode location.

Low frequency stimulation (0.5 Hz) was applied to the abdominal muscles of 10 able bodied and five tetraplegic participants. The electrode positions which achieved the strongest muscle contractions were recorded as the motor point positions, with measurements repeated once. For five able bodied participants, assessments were repeated after 18 months, in seated and supine positions.

Intersubject uniformity ranged from 2.8 to 8.8%. Motor point positions were identified with intrasubject repeatability of <1.7 cm, deemed adequate relative to standard AFES electrode size. Intrasubject repeatability shows motor point positions changed little (<1.7 cm) after 18 months but varied between seated and supine positions with repeatability of up to 3.1 cm.

A simple technique to locate the motor points of the abdominal muscles is presented and shown to have an adequate intrasubject repeatability, enabling the optimum AFES electrode location to be identified for each user.